The reliance placed on various electronic devices by people increases with technological progress. For most electronic devices, such as desk computers and notebook computers, electronic elements thereof will produce a large quantity of heat when they operate. The produced heat must be timely guided away from the electronic devices to avoid the problem of overheating.
Taking a computer as an example, it internally includes some heat-producing elements, including but not limited to a central processing unit (CPU) and a power supply. When the computer is in use, the CPU produces a high amount of heat when it performs operation for data processing at a high speed. The produced heat renders the CPU in an unstable state, which might cause the computer to crash in some less serious conditions. However, in some worse conditions, the produced heat could result in burnout or damage of the CPU.
Presently, a general way for solving the problem of heat dissipation is to provide at least one cooling fan in the computer, so that the heat produced by the CPU can be quickly guided to a space outside the computer by the cooling fan through forced heat dissipation.
Generally, a cooling fan uses a single-phase alternating-current (AC) motor. For a single-phase induction motor, a single-phase power does not produce a rotating magnetic field. More specifically, the single-phase power produces a magnetic field that is changeable in its magnitude but not in its direction and therefore can not be used to start the fan's motor. Therefore, the magnetic field produced by supplying the alternating current to a stator coil of the fan motor should not be a fixed magnetic field but a changeable magnetic filed that has N pole and S pole changed with time. By taking advantage of this characteristic, it is possible to design a surrounding magnetic field that can push a rotor of the fan motor at different times and from different positions, so that the rotor rotates continuously.
For this reason, the single-phase power supplied to the single-phase induction motor must be converted into a two-phase power for starting the motor. Therefore, in the single-phase induction motor, there must be at least two-phase windings. The process of converting single-phase power into two-phase power is referred to as phase splitting. There are two types of single-phase AC motors, namely, resistance-start induction motor and capacitance-start motor, each of which performs phase-splitting in a different way. And the capacitance-start induction motor is more common in use.
A main structural form of the capacitance-start induction motor is the two-phase AC motor, which is characterized by having a capacitance applied across the motor wiring consisting of silicon steel plates and coils to create a phase shift, so that a phase difference occurs in the power supplied to the electrical magnets so formed to drive the motor to rotate.
Generally, the capacitance-start induction motor has somewhat poor energy conversion efficiency mainly because its major elements, such as the silicon steel plates, the coils, the capacitor elements and the voltage all are unchanged. As a result, the capacitance-start induction motor fails to have increased rotational speed and can not control its output power according to requirements. These problems in turn adversely influence the fan's heat dissipation and ventilation effects.